At the present time, most refrigeration systems utilize two partially miscible fluids; a refrigerant for heat transfer, and a lubricant for lubricating machine elements in the compressor, such as bearings and the like. The lubricant is necessary because refrigerants typically do not have adequate viscosity or lubricity for lubrication purposes. Because it is impractical to completely seal the two fluids from each other within the compressor, refrigeration systems are designed to manage the degree and locations where the mixing of these two fluids can occur. Compressors typically have a separate sump, pumping means, and distribution system for the lubricating oil, all isolated, but not sealed from the refrigerant. Pressure, temperature and mechanical separation means are employed to maintain a sufficiently oil rich mixture in the sump for reliable lubrication, typically no more than 20% refrigerant by weight. Refrigeration systems are also designed to limit the amount of oil discharged into the heat transfer devices, such as the evaporator, to avoid fouling and associated loss of system efficiency. Solubility characteristics between the fluids are tailored to minimize the amount of dissolved refrigerant in the oil sump, yet provide sufficient solubility in the evaporator, condenser, and interconnecting piping to assure oil leaving the compressor returns via entrainment in the circulating refrigerant.
The need to maintain an oil rich fluid in the sump, and limit the build up of oil in the evaporator, over the wide range of operating conditions common in refrigeration systems, usually necessitates complex and costly control systems and fluid separation features. Loss of control of the two fluids during extreme system operating conditions is a common cause of compressor failures, particularly compressor bearing failures, due to excessive refrigerant buildup in the sump. For these reasons, efforts have been directed to elimination of the need for oil separation, and to use the refrigerant rich lubricating fluids naturally residing in the evaporator or condenser for lubrication purposes.
A typical refrigeration system includes a compressor, condenser, expansion valve, and evaporator. Compressed refrigerant rich gas typically containing less than 2% oil is discharged from the compressor into a condenser where heat rejection transforms the refrigerant into a liquid. The mixture then passes through an expansion valve into the evaporator, where absorbed heat transforms the liquid mixture back into a gaseous refrigerant and liquid oil. As the mixture is discharged from the compressor, the oil is mechanically separated into a sump and the refrigerant is channeled into the compression process. In the specific case of oil flooded screw compressors, the mixture of oil and refrigerant discharged from the compressor is passed through an oil separator, where droplets containing 80% oil/20% refrigerant are collected for lubrication and oil sealing purposes.
Various efforts have been reported in the prior art to use oil and refrigerant mixtures as part of a lubrication system. Zimmern et al. U.S. Pat. No. 4,589,826 proposes a method of lubricating bearings in a compressor in which a refrigerant gas loaded with oil in the form of a mist is delivered to the bearings. This system requires a two phase system of gaseous refrigerant and oil droplets, and requires equipment to mix a known quantity of oil in a refrigerant gas.
The parent application of Zimmern et al., Noda et al. U.S. Pat. No. 4,553,399 discloses transferring a liquid refrigerant having oil dissolved therein to a casing of the compressor motor to vaporize the refrigerant, to form a two phase mixture with oil droplets in a gas mixture. The two phase mixture is then transferred to the bearings or other parts needing lubrication. In an alternative embodiment, the oil itself is transferred to the bearings after the gaseous refrigerant has been removed by vaporization using the heat of the motor. In both Noda et al. and Zimmern et al., attempts are made to lubricate bearings with gaseous refrigerants and droplets of lubricating oil, typically in concentrations of less than 2% or 3% by volume of oil.
One of the earliest designs for refrigeration machines having lubrication is disclosed in Stair U.S. Pat. No. 1,195,162. In the Stair patent, the lubricant is separated from the refrigerant by centrifugal force, one of many means of separation of oil from refrigerant that may be used.
Finally, two patents to Shaw, U.S. Pat. Nos. 4,375,156 and 4,439,121, disclose transfer of oil in a mist form, representing a two phase mixture of oil mist in gaseous refrigerant.
Accordingly, it is an object of this invention to provide an improved device, system and method for lubricating bearings and the like in refrigerant devices such as refrigerant compressors.
Another object of the present invention is to provide a device, system and method for using the oil contained in liquid refrigerant to lubricate bearings utilizing the heat generated by the bearing as the refrigerant vaporizing means and the like which in accordance with the preferred embodiment of the invention without use of expensive and complicated separation devices.
Other objects will appear hereinafter.